Objectives: (a) To evaluate the serologic response to infection with B. pertussis and immunization with pertussis vaccine (b) To determine which serologic assays have the highest diagnostic sensitivity and specificity for pertussis and (c) To understand pertussis epidemiology in the community through seroprevalence and outbreak studies. (1) CDC Multicenter Surveillance Study: Evaluation of data collected for this study has continued. (2) Serodiagnosis: (a) Assays are in place to measure IgG, IgA, and IgM antibodies to PT, FHA, LOS, 69kDa protein, fimbriae, and whole bacteria. These 18 assays plus the whole-cell microagglutination assay have been performed on paired sera from forty culture positive pertussis cases, 25 children immunized with whole-cell vaccine and 52 normal controls. The goal is to select the assays with the highest sensitivity and specificity for pertussis serodiagnosis. No single assay has the required characteristics and analyses are underway to select the optimal combination of assays. (b) Historical data have shown that for children immunized with whole-cell vaccine, pertussis agglutinating antibodies correlated with clinical protection. Analysis of the serologic data indicates that IgG anti-fimbriae antibodies correlate best with agglutinins in immunized children while IgG and IgA anti-fimbrial antibodies correlate well with agglutinins in convalescent individuals. (c) Although a high percentage of pertussis patients make a response to B. pertussis LOS, the specificity of this response in pertussis has not been demonstrated. Studies are underway to determine if there is immunologic cross-reactivity between the B pertussis LOS and the LOS from other gram negative bacteria. (3) Seroepidemiology: ELISA and agglutination assays were performed on about 150 sera obtained from foreign health officials to evaluate pertussis prevalence to assess the suitability of these sites for pertussis vaccine efficacy trials.